Method of making hollow cast articles from metal alloys having long freezing ranges

ABSTRACT

A technique for improving the physical properties of thin walled castings and reduction or avoidance of hot tearing in such castings involves casting in the inverted position, preferably using no core. The exterior of the casting is contoured to the shape of a metal mold which causes rapid solidification with resultant improved soundness and improved physical properties. Metal is then removed from the interior of the casting for example by machining to form the desired wall thickness.

United States Patent [19] v Krock et al.

Appl. No: 217,014

[73] As'signee:

U.S Cl...; 29/526.5, 29/527.5 29/527.6,

Int. Cl. 322d 2.7/04

Field of Search 164/69, 126; 29/526.4,

References Cited UNITED STATES PATENTS 12/1970 Richmond et a1. 164/68 IA technique for improving the physical properties of 1451 May 7,1974

11/1926 Otto... ..29/526.4 ux 1/1971 $1. 01111; l64/69X PrimaryExaminer-Charles W. Lanham Assistant Examiner-'D. C. Reiley, lllAttorney, Agent,- or Firm-Richard H. Childress; Charles W. Hoffmann;Robert F. Meyer ABSTRACT thin walled castings and reduction or avoidanceof hot tearing in such castings involves casting in the invertedposition, preferably using no core. The exterior of the casting iscontoured'to the shape of a metal mold which causes rapid solidificationwith resultant improved soundness and improved physical properties.Metal is then removed from the interior of the casting for example bymachining to form the desired wall thickness.

6 Claims, 4 Drawing Figures PA TENTEII 7 I974 PRIOR ART FINE. 2

ALU M I NUM BERYLLIUM PHASE DIAGRAM WEIGHT PER CENT BERYLLIUM O m 9 o lm4 O OIQ 9 7 O- 6 0 O 8 5 O- .m 4 I O 6. 3 v m 0 M 5 O- 2 O 4 RIJI O 25- w mm III] IIIIO 2 6 I. i o O. I k O O O O 0 O O OO O 0 O O O O O O OO B m m w 9 a w s w w 1 METHOD OF MAKING HOLLOW CAST ARTICLES FROM METALALLOYS HAVING LONG FREEZING RANGES The invention described herein wasmade in the course of, or under, a subcontract issued under PrimeContract W-7405-ENG-48 with the United States Energy Commission.

SUMMARY OF THE INVENTION The following method is used to improve thephysical properties of relatively thin walled hollow castings andprevent hot tearing caused by cores in alloys having long freezingranges. The casting is inverted from the normal casting position andpreferably no core is used, The exterior of the casting is contoured tothe shape of a metal mold which causes rapid soldification withresultant improved soundness and high physical properties. The centersection acts as a riser to feed the outer shell and minimizeinterdentritic shrinkage and hot tearing. The interior is then machinedout to form the desired wall thickness.

DRAWINGS FIG. 1 is a view of a mold set up for the casting of-hollowsections according to the prior art.

FIG. 2 is a sectional view of the coreless casting method according tothe present invention.

FIG. 3 is a view of a casting produced in accordance with the presentinvention.

FIG. 4 is a view of the beryllium-aluminum phase diagram illustratingthe long freezing of this system.

BACKGROUND OF THE INVENTION In accordance with techniques of the priorart, alloys having long freezing ranges have been difficult to cast inthin section sizes in hollow configurations. The problems involvedinclude hot tearing of the metal during casting. Also the resultingcastings often contain shrinkage resulting from the difference indimensions between the material when first cast as compared to the roomtemperature dimensions.

The common method of casting hollow members with alloys having longfreezing ranges is shown in FIG.

-1. A metal mold 10 made for example, of copper, steel or graphiteincludes a base portion 11, a cylindrical portion' 12, and a core 15 isutilized to form the casting. If desired an insulating sleeve 17 forexample, made of alumina or zirconia also can be used to define a hottop portion 18. Alternatively the hot top portion may be defined by theinterior surface 13 of material 12. Water cooling systems (not shown)are sometimes utilized in connection with the prior art construction ofFIG. 1.

However, with or without water cooling, hot tearing has always been aproblem in casting according to the prior art construction with alloyshaving a long freezing range. Additionally, interdentritie shrinkage andshrinkage resulting from the dimensional differences between the as castmaterial and the material at lower room temperature are seriousproblems.

In accordance with the present invention it has been found that if thecasting is inverted from the position shown in FIG. 1 and the core isnot used the problems of shrinkage and hot tearing are eliminated or aresubstantially reduced.

As shown in FIG. 2, a mold 100 may be used having a base portion 101 anda cylindrical portion 102. Base portion 101 defines the external surfaceof the casting at 103. The preferred mold material or the mold is metaland most preferably it is made of steel, copper, or cast iron. Graphitemay also be used if desired.

A hot top section is provided in conjunction with portion 102. Ifdesired an insulating sleeve 121 may be provided which may be made offor example alumina or zirconia.

While not being wished to be bound by any particular theory, it isbelieved that the improvements observed according to the castingtechnique of the present invention are achieved because the massive moldsection 101 removes heat very rapdily as a result of which rapidsolidification occurs at and near the surface 103. The center section134 of casting acts as a riser to feed the outer shell 131. As a resultinterdentritic shrinkage and hot tearing are minimized, and goodphysical properties are obtained at and near the surface of the casting,particularly for wall thickness less than about onehalf inch.

After the casting operation the casting 130 is removed from the mold andis machined to desired dimensions. If desired the casting may be simplycropped off along the line 132 of FIG. 3, and then the leg portion 131machined as illustrated, removing center section 134. Alternatively itmay be desirable for the leg portion 131 to be longer including portion135 in which case the casting will not be cropped at 132 and themachining will include the portion 137, as illustrated.

Obviously the particular casting configurations shown are by way ofexample, only, and a wide variety of configurations may be cast andmachined to desired shape according to the present invention.

The present invention is applicable to a wide variety of alloys having along freezing range, generally having a freezing range of at least about500 C and preferably above 550 C. Examples include the beryliumaluminumsystem shown in FlG. 4, incluing alloying additives such as copper,magnesium, silicon, precious metals, either singly or in combination,preferably not totaling above about 10 percent, which may be used forvarious purposes such as strengthening the aluminum matrix andfacilitating nucleation during casting. The preferred alloys containabout 80 to about 95 atomic percent beryllium.

Additional alloying systems include aluminumgermanium perferably about90-to 99'atomic percent germanium, gold-germanium preferably 85 to 99atomic percent germanium, lead-germanium preferably 75 to 99 atomicpercent germanium, galliumgermanium preferably 20 to 99 atomic percentgermanium, silver-silicon preferably 65 to 99 atomic percent silicon andsilicon-tin preferably 10 to 99 atomic percent silicon.

Insofar as preparing the molten metal for casting is concerned, a widevariety of techniques are available As an example of the presentinvention, a berylliumaluminum alloy containing 75 weight percentberyllium about 24.7 weight percent aluminum alloy and about 0.3 percentplatinum was heated to a melting temperature of about l,400 C and wasthen poured into the mold shown in FIG. 2 at about 1,200 C. A similarcom-' position was poured into the mold shown in FIG. I having beenheated to the same melting and pouring temperatures, and otherwisesimilarly processed.

The resulting mechanical properties for the alloy cast in the mold shownin FIG. I was 19,000 psi ultimate tensile strength; 0.2 percent yieldstrength, 18,000 psi from a tensile bar taken near the surface of core15. Radiography revealed extreme shrinkage and porosity adjacent thecore in the resulting casting.

The castings produced according to the design in FIG. 2 had a tensilestrength of 32,000 psi and 25,000 psi 0.2 percent yeild strength from atensile bar taken from section 131. Radiography revealed very littleshrinkage and porosity in the channel portion formed adjacent surface103 in the lower portion of the mold 101.

What is claimed is:

l. A method of making a relatively thin walled hollow tapered castarticle from molten metal having an extremely long freezing range, themethod comprising the steps of feeding molten metal having a freezingrange of about 500 C or longer into a mold having an inverted taperedmold cavity and having a massive tapered bottom portion capable ofwithdrawing heat more rapidly from molten metal than an adjacentinsulated upper portion of the mold, solidifying ,molten metal in themassive bottom portion of the mold where heat is more rapidly withdrawnfrom the molten metal than withdrawn in the adjacent insultated portionof the mold and wherein molten metal at about the center of the moldacts as riser means and then solidifying the remainder of the moltenmetal in the mold to form a solidified casting of solid tapercross-section containing a minimum of hot tearing, removing thesolidified casting from the mold, and removing solidified metal from theinterior of the solidified casting to form the hollow cast article.

2. The method of claim 1, wherein the molten material having a freezingrange of about 500 C or longer is a molten alloy selected from the groupconsisting of Be base alloys, Si base alloys or Ge base alloys.

3. The method of claim 2, wherein the molten alloy is a Be base alloycontaining Al.

4. The method of claim 1, wherein the molten material is poured into themold. I

5. The method of claim I, wherein the mold is a coreless mold.

6. The method of claim 5, wherein the solidfied castshrinkage.

UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No.3808671 Dated Ma 7 1974 Inventofl Richard H. Krock & William J. RichmondIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Col. 1, line 7, after "States" insert ---Atomic-.

Col. 1, line32, after "freezing" insert -range-.

Col. 2, line 13, change "rapdily" to --rapid1y-.

Col. 4, line 4, after "than" insert -is--.

Signed and sealed this 10th day of September 1974.

(SEAL) Attest:

McCOY GIBSON, JR. I C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-1050 (10-69) USCOMWDC 6037mm U. 5. GOVERNMENT PRINTINGOFFICE: I969 0-366-334,

1. A method of making a relatively thin walled hollow tapered castarticle from molten metal having an extrely long freezing range, themethod comprising the steps of feeding molten metal having a freezingrange of about 500* C or longer into a mold having an inverted taperedmold cavity and having a massive tapered bottom portion capable ofwithdrawing heat more rapidly from molten metal than an adjacentinsulated upper portion of the mold, solidifying molten metal in themassive bottom portion of the mold where heat is more rapidly withdrawnfrom the molten metal than withdrawn in the adjacent insultated portionof the mold and wherein molten metal at about the center of the moldacts as riser means and then solidifying the remainder of the moltenmetal in the mold to form a solidified casting of solid tapercross-section containing a minimum of hot tearing, removing thesolidified casting from the mold, and removing solidified metal from theinterior of the solidified casting to form the hollow cast article. 2.The method of claim 1, wherein the molten material having a freezingrange of about 500* C or longer is a molten alloy selected from thegroup consisting of Be base alloys, Si base alloys or Ge base alloys. 3.The method of claim 2, wherein the molten alloy is a Be base alloycontaining A1.
 4. The method of claim 1, wherein the molten material ispoured into the mold.
 5. The method of claim 1, wherein the mold is acoreless mold.
 6. The method of claim 5, wherein the solidfied castingof the alloy experiences a minimum of interdentritic shrinkage.